Within a communications network, a variety of communication scenarios can co-exist. For example, a radio can be configured to be a member of a group of radios (also referred to herein as a talkgroup, which in addition to voice, may carry data, audio, and/or video), wherein a single radio may transmit information that is substantially simultaneously received by other members of the talkgroup. In some cases, a radio participating in a talkgroup may transmit information to and/or receive information from other radios in the talkgroup without the use of fixed infrastructure for controlling call establishment, call flow and call tear-down functions. That is, all call parameters including addresses, frequencies used, and basic operating attributes are pre-configured in the radio to enable initial connections to the talkgroup. This method of communication among radios in the talkgroup is referred to herein as direct communication. In other cases, the radio may transmit information to and/or receive information from other radios in the talkgroup via a repeater, for example a base station. In these cases, the radio may transmit information to the base station on a first frequency and the base station may further transmit the information to other radios in the talkgroup on a second frequency. This method of communication is referred to herein as conventional communication.
Talkgroup radio communications are widely used by, for example, public safety users. A radio may subscribe to one or more talkgroups, each of which is assigned to a specific frequency channel or pair of channels. When the radio is associated with more than one talkgroups, the radio is typically pre-configured to include an identifier for each associated talkgroup and the specific frequency channel(s) assigned to the associated talkgroup. In other words, for every talkgroup out of a predefined number talkgroups associated with the radio there is exactly one frequency channel or pair of channels from a set of frequency channels that the talkgroup is mapped to and the radio may be configured to include the talkgroup identifier and the associated frequency channel(s). For example, if there are three talkgroups—talkgroup 1, talkgroup 2, and talkgroup 3, each of which is assigned a respective frequency channel from a set of three frequency channels, then talkgroup 1 may be assigned to frequency channel 1, talkgroup 2 may be assigned to frequency channel 2, and talkgroup 3 may be assigned to frequency channel 3. During use, a radio associated with the three talkgroups may select one of the three talkgroups at any point in time. Upon selecting a talkgroup, the radio can use the assigned talkgroup frequency channel to transmit information to and/or receive information from other radios on the selected talkgroup.
In its basic operation, if the radio selects talkgroup 1, the radio is configured to monitor the corresponding frequency channel for talkgroup 1 (frequency channel 1) to detect call establishment on talkgroup 1. Accordingly, the radio is configured to receive and/or transmit information only on the selected talkgroup, i.e., talkgroup 1, until the radio selects another talkgroup, for example talkgroup 2, and tunes to the frequency channel assigned to talkgroup 2. Hence, while talkgroup 1 is selected, the radio cannot simultaneously monitor other talkgroups and the radio may miss information transmitted on these other talkgroups. One approach to overcoming this limitation allows for the radio to periodically switch between associated talkgroups to detect activity on a subset or any of the pre-programmed talkgroups. The limitations associated with switching between talkgroups are a direct function of, for example, how long it takes the radio to tune in to a new frequency channel, how long the radio has to stay on the frequency channel to detect a signal, how long it takes the radio to perform synchronization of time and frequency, or how long it takes the radio to recover any additional parameters that will enable decoding of information that the radio will use to determine what type of radio activity is present on a particular frequency channel. Because of these switching limitations, during the time it takes the radio to switch between talkgroups, the radio cannot monitor either one of the talkgroups. Therefore, during switching periods, the radio is subject to missed talkgroup communications. In addition, when call information is detected on the selected talkgroup, all other talkgroups will not be monitored for the duration of the call and the radio is subject to missed call information transmitted on other talkgroups while receiving call information on the selected talkgroup.
In some cases, multiple talkgroups may be assigned to the same frequency channel. For example, if there are thirty talkgroups and three frequency channels, talkgroups 1-10 may be assigned to frequency channel 1, talkgroups 11-20 may be assigned to frequency channel 2, and talkgroups 21-30 may be assigned to frequency channel 3. When an assigned frequency channel is in use, radios associated with other talkgroups that are also assigned to the currently used frequency channel cannot initiate calls on the other talkgroups, even if another frequency channel is available. Consider the following example where a call is established on talkgroup 1 using frequency channel 1. While the call is taking place on talkgroup 1, radios associated with talkgroups 2-10 that are also mapped to frequency channel 1 cannot initiate calls on talkgroups 2-10 as those calls will conflict with the ongoing call of talkgroup 1 and create destructive radio interference that can result in poor communications for radios operating in all talkgroups on the selected frequency channel. Even if frequency channel 3 is available, radios associated with talkgroups 2-10 cannot initiate calls on talkgroups 2-10 using frequency channel 3. Taking this example further, if a member of talkgroup 1 experiences an emergency during a period when another talkgroup 1 member is transmitting on frequency channel 1, in the current configuration if the member experiencing the problem attempts a new transmission on frequency channel 1 at the same time that the other member is sending an ongoing transmission on the frequency channel, the new transmission will be rejected, or if not rejected, interfere with the ongoing transmission.
Accordingly, there is a need for an improved method and apparatus for allocating frequencies among multiple talkgroups.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.